1. Field of the Invention
The present invention relates to a portable tool for hand-finishing concrete. In particular, the invention relates to a rotary attachment to a hand-held powered tool for finishing concrete.
2. Description of the Related Art
Construction of buildings and other civil works typically involve the use of concrete. Construction using concrete involves the tasks of first placing and then, usually, finishing the concrete. Placing concrete involves pouring or otherwise placing concrete, while in a fluid state, into forms having the desired shape of the finished, cured concrete product. Finishing concrete involves treatment of the exposed surface of the concreted after pouring into the forms to achieve a desired texture and surface hardness.
Concrete is a mixture of cement, aggregates and water. The aggregates are comprised of various grades of sand or gravel, and are selected dependant upon the desired final properties, such as strength, smoothness and cost of the final concrete product. The cement acts as a binder between the aggregate particles. The cement, typically Portland cement, is comprised principally of calcium oxide, which is produced by roasting calcium carbonate, found in common minerals such as limestone and chalk. When the finished cement is mixed with water, the calcium oxide undergoes the chemical reaction of hydration, producing a hard crystalline structure around the particles of the aggregate, cementing them together.
The first step in the concrete construction process is to mix the concrete ingredients. Cement, water and aggregates are placed in a mixer and blended to evenly disperse the ingredients and thoroughly wet the cement, producing a fluid slurry. The mixing process can be accomplished at the construction site by mixing the ingredients in a portable cement mixer. More commonly, though, it is accomplished in a concrete mixing truck at a central plant. The concrete ingredients are added to the truck at the central plant, and the ingredients are mixed and blended while the truck is en route to the construction site.
Once the concrete is mixed and transported to the construction site, the concrete still in a slurry state, is placed within pre-constructed forms. Once placed within forms, the concrete is consolidated and finished. Consolidating the concrete is accomplished using a solid or vibratory rod which is inserted into the placed concrete, and assures that the concrete slurry fills all voids within the concrete forms and no air bubbler or rock pockets remain.
The final step in concrete construction is finishing of the placed, consolidated concrete. Finishing typically involves the steps of screeding, floating and troweling the concrete. Screeding involves leveling the surface of the poured concrete slurry across the top edges of the forms, producing a flat, though rough surface. Screeding removes any humps or hills and fills in any depressions or voids in the surface. Screeding is following by floating, a process which provides a smoother, harder surface than that remaining after the screeding process. Floating is done after the concrete has begun to harden but is still in a plastic state. Floating uses a tool called a float or bull float, typically made with a flat plate of aluminum, magnesium, wood or rubber. A small handle is attached parallel to the upper surface of the float. An operator holds the handle and sweeps the lower surface of the float across the surface of the screed concrete. For larger areas, a bull float is used, which has a longer plate and a long pole handle disposed at an angle to the upper surface of the plate.
The next step in concrete finishing is troweling, in which the floated surface is troweled to force downward any large surface aggregate particles and to produce an even harder, denser, smoother surface. Troweling can be accomplished using a hand trowel or a troweling machine. The hand trowel is comprised of a small, flat, rectangular metal sheet with a handle disposed parallel on the upper surface of the metal sheet. Troweling by hand is accomplished by holding the handle in one hand, pressing the undersurface of the trowel against the concrete surface, applying a slight torque to the handle to apply greater pressure on the trailing edge of the trowel, and then sweeping the trowel across the surface of the concrete. With practice, an operator learns the correct amount of pressure and torque to apply to the trowel handle to achieve the desired surface finish.
The troweling machine is generally comprised of a vertical shaft motor or engine with typically four flat, horizontal blades disposed orthogonally at the lower end of the motor shaft. Each blade is slightly canted from the direction of rotation to lower its trailing edge. A handle assembly is disposed at the upper end of the engine for controlling the troweling machine by an operator. The engine rotates the blade assembly across the surface of the concrete, which quickly smoothes and finishes the concrete before it fully hardens. The troweling machine can finish larger areas of concrete surfaces more quickly and with less labor than is possible by traditional hand troweling. However, the size of the troweling machine, in which the blade assembly typically has a diameter of three feet or more, precludes its use on smaller areas, such as on treads of concrete stairs, on the top edges of curbs, on concrete countertops and other surfaces with limited size or access. In these circumstances, a motorized system for troweling is desirable to increase productivity over hand troweling yet capable of reaching small or confined surfaces not presently accessible by larger troweling machines.
Several hand tools are commercially available which could be adapted as a portable powered concrete finisher. For example, an angle grinder has an elongated body containing an electric or pneumatic motor which is small and light enough to be held by hand. At the front end of the angle grinder is disposed a spindle orientated orthogonally to the major axis of the body of the grinder. A variety of circular attachments may be mounted on this spindle, such as grinding wheels, abrasive cutoff wheels, sanding disks and buffing and polishing wheels. However, no attachment is presently available in the prior art which is capable of troweling concrete.